Laser-sintering powder with PMMI, PMMA, and/or PMMI-PMMA copolymers, process for its preparation, and moldings produced from this laser-sintering powder

ABSTRACT

The present invention relates to a sinter powder composed of polyamide which also comprises PMMI, PMMA, or copolymers with PMMI, in particular PMMI-PMMA copolymers, to the use of this sinter powder for laser-sintering, and also to moldings produced from this sinter powder. The moldings made from the powder of the invention have marked advantages over conventional products in their appearance and in their surface quality, especially as far as roughness and dimensional stability during selective laser sintering (SLS) are concerned. In addition, moldings produced from the sinter powder of the invention also have better mechanical properties than moldings based on conventional nylon-12 powders, in particular in terms of modulus of elasticity and tensile strength. These moldings also have a density close to that of injection moldings.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a laser-sintering powder based onpolyamide, preferably nylon-12, which comprises PMMI (particles), orPMMA (particles), or PMMI-PMMA copolymer (particles), to a process forpreparing this powder, and also to moldings produced by the selectivelaser-sintering of this powder.

[0003] 2. Discussion of the Background

[0004] In very recent times, a task which is often encountered is therapid production of prototypes. Selective laser-sintering is a processparticularly well suited to rapid prototyping. In this process, polymerpowders in a chamber are selectively irradiated briefly with a laserbeam, resulting in melting of the particles of powder on which the laserbeam falls. The molten particles fuse and solidify again to give a solidmass. Three-dimensional bodies can be produced simply and rapidly bythis process, by repeatedly applying fresh layers and irradiating these.

[0005] The process of laser-sintering (rapid prototyping) to realizemoldings made from pulverulent polymers is described in detail in thepatent specifications U.S. Pat. No. 6,136,948 and WO 96/06881 (both DTMCorporation). A wide variety of polymers and copolymers can be used forthis application, e.g. polyacetate, polypropylene, polyethylene,ionomers, and polyamide.

[0006] Nylon-12 powder (PA 12) has proven particularly successful inindustry for laser-sintering to produce moldings, in particular toproduce engineering components. The parts manufactured from PA 12 powdermeet the high requirements demanded in respect of mechanical loading,and therefore have properties particularly close of those of themass-production parts subsequently produced by extrusion or injectionmolding.

[0007] A PA 12 powder with a good suitability here has a median particlesize (d₅₀) of from 50 to 150 μm, and is obtained as in DE 197 08 946 orelse DE 44 21 454, for example. It is preferable here to use a nylon-12powder with a melting point of from 185 to 189° C., an enthalpy offusion of 112±17 J/g, and a freezing point of from 138 to 143° C., asdescribed in EP0911 142.

[0008] Although the properties of the known polymer powders are indeedgood, moldings produced using these powders still have somedisadvantages. Particular disadvantages with the polyamide powderscurrently used are rough surfaces on the moldings, these resulting fromthe boundary between particles which have undergone melting or incipientmelting and the surrounding particles which have not undergone melting.In addition, the formation of extended crystallite structures on coolingof the moldings from polyamide sinter powder is disadvantageous insofaras it is found to give increased shrinkage, or even warpage of theparts. Relatively large components, or components where there is somehindrance to shrinkage, are particularly susceptible to warpage. Thevery rough surfaces require a coating if parts of suitable quality areto be obtained. In addition, the roughness of the surface causes smallstructures to merge, making their resolution unsatisfactory.

[0009] It was therefore an object of the present invention to provide alaser-sintering powder which can give better dimensional stability andsurface quality in the parts produced by means of selectivelaser-sintering.

[0010] Surprisingly, it has now been found that addition ofpoly(N-methylmethacrylimide) (PMMI), polymethyl methacrylate (PMMA),and/or PMMI-PMMA copolymer to polyamides can produce sinter powders fromwhich, by laser-sintering, it is possible to produce moldings which havemarkedly better dimensional stability and smoothness than moldings madefrom conventional sinter powders.

SUMMARY OF THE INVENTION

[0011] Accordingly, it is an object of the present invention to providea sinter powder for selective laser sintering, which comprises at leastone polyamide and at least one PMMI, at least one PMMA, and/or at leastone PMMI-PMMA copolymer.

[0012] It is another object of the present invention to provide aprocess of preparing sinter powder of the invention, which comprisesmixing at least one polyamide with PMMI, PMMA, and/or PMMI-PMMAcopolymer, to give a sinter powder.

[0013] Additionally, it is another object of the present invention toproduce moldings that are produced by laser sintering sinter powders,which comprise PMMI, PMMA, or PMMI-PMMA copolymer, and at least onepolyamide.

[0014] The sinter powder of the invention has the surprising advantagethat moldings produced therefrom by laser sintering have a very smoothsurface. Even small structures, such as inscriptions, have very goodresolution. This opens up application sectors which hitherto wereinaccessible due to poor resolution.

[0015] The very good dimensional stability of the components enormouslyimproves the reliability of the process, because it is possible toreproduce the desired dimensions directly in the first step. This isoften not the case when conventional powders are used, the result beingwarpage of components when they are first manufactured, and the need torepeat the sintering process using different process parameters ordifferent placing within the manufacturing chamber.

[0016] Surprisingly, it has been found that moldings produced from thesinter powder of the invention have equally good or even bettermechanical properties in particular in terms of modulus of elasticity,tensile strength, and density.

[0017] The sinter powder of the invention, and also a process for itspreparation, are described below, but there is no intention of anyresultant restriction of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] A feature of the sinter powder of the invention for selectivelaser-sintering is that the powder comprises at least one polyamide andat least one PMMI, PMMA, PMMI-PMMA copolymer, preferably a PMMI-PMMAcopolymer. The polyamide present in the sinter powder of the inventionpreferably comprises a polyamide which has at least 8 carbon atoms percarboxamide group. The sinter powder of the invention preferablycomprises at least one polyamide which has 10 or more carbon atoms percarboxamide group. The sinter powder very particularly preferablycomprises at least one polyamide selected from nylon-6,12 (PA 612),nylon-11 (PA 11), and nylon-12 (PA 12), or copolyamides based on theabovementioned polyamides. The sinter powder of the invention preferablycomprises an unregulated polyamide.

[0019] A nylon-12 sinter powder particularly suitable forlaser-sintering is known whose melting point is from 185 to 189° C.,preferably from 186 to 188° C., and whose enthalpy of fusion is 112±17J/g, preferably from 100 to 125 J/g, and whose freezing point is from133 to 148° C., preferably from 139 to 143° C. The process for preparingthe polyamide powders on which the sinter powders of the invention arebased is well-known and in the case of PA 12 may by way of example befound in the specifications DE 29 06 647, DE 35 10 687, DE 35 10 691 andDE 44 21 454, the content of which is incorporated into the disclosurecontent of the present invention by way of reference. The necessarypolyamide pellets may be purchased from various producers, and by way ofexample nylon-12 pellets are supplied by Degussa AG with the trade nameVestamid®.

[0020] Another nylon-12 particularly suitable is one which has a meltingpoint from 185 to 189° C., preferably from 186 to 188° C., and whoseenthalpy of fusion is 120±17 J/g, preferably from 110 to 130 J/g, andwhose freezing point is from 130 to 140° C., preferably from 135 to 138°C., and whose crystallization temperature after aging is preferably from135 to 140° C. These properties were determined as described in EP 0 911142, by means of DSC. The method of aging was storage at 150° C. for 7days in a VT 5142 EK vacuum drying cabinet from Heraeus. Nylon-12powders which have these properties are described by way of example inDE 102 55 793, and preferably comprise metal soaps.

[0021] Based on the entirety of the polymers present in the powder, thesinter powder of the invention preferably comprises from 0.01 to 30% byweight of at least PMMI, PMMA, and/or PMMI-PMMA copolymer, withpreference from 0.1 to 20% by weight of PMMI, PMMA, and/or PMMI-PMMAcopolymer, with particular preference from 0.5 to 15% by weight of PMMI,PMMA, and/or PMMI-PMMA copolymer, and with very particular preferencefrom 1 to 12% by weight of PMMI, PMMA, and/or PMMI-PMMA copolymer. Theranges stated here are based on the total content of PMMI, PMMA, andPMMI-PMMA copolymer in the powder, where powder means the entire amountof components. The sinter powder of the invention may comprise a mixtureof particles of PMMI, particles of PMMA, and/or particles of PMMI-PMMAcopolymer with particles of polyamide, or else comprise polyamideparticles or, respectively, powder into which PMMI, PMMA, and/orPMMI-PMMA copolymer has been incorporated. If the content of PMMI, PMMA,and/or PMMI-PMMA copolymer, based on the entirety of the polymerspresent in the powder, is below 0.01% by weight, there is a markedreduction in the desired effect providing dimensional stability andsurface quality. If the content of PMMI, PMMA, and/or PMMI-PMMAcopolymer, based on the entirety of the polymers present in the powder,is above 30% by weight, the mechanical properties become markedlypoorer, e.g. the tensile strain at break of moldings produced from thesepowders.

[0022] If the sinter powder comprises a mixture of polyamide particlesand particles of PMMI, particles of PMMA, and/or particles of PMMI-PMMAcopolymer, the preferred median particle size of polyamide particles isfrom 10 to 250 μm, preferably from 40 to 100 μm, and particularlypreferably from 45 to 80 μm. The size of the particles of PMMI,particles of PMMA, and/or particles of PMMI-PMMA copolymer is preferablywithin 20%, with preference within 15%, and very particularly preferablywithin 5%, of the median grain size d₅₀ of the polyamide particles or,respectively, polyamide powders. The grain size is in particular subjectto a limit by virtue of the permissible overall height or, respectively,layer thickness in the laser-sintering apparatus.

[0023] If the sinter powder comprises particles which comprise not onlypolyamide but also at least one PMMI, PMMA, and/or PMMI-PMMA copolymer,the median grain size d₅₀ of the particles is preferably from 10 to 250μm, with preference from 40 to 100 μm, and particularly preferably from45 to 80 μm.

[0024] The poly(N-methylmethacrylimides) (PMMI), polymethylmethacrylates (PMMA), and/or PMMI-PMMA copolymers present in the sinterpowder of the invention are preferably copolymers of PMMI and PMMA whichare prepared by partial cycloimidization of the PMMA. (The usual methodof preparing PMMI via partial imidization of PMMA is to imidize no morethan 83% of the PMMA used. The resultant product is termed PMMI, but isstrictly a PMMI-PMMA copolymer). Both PMMA and PMMI or PMMI-PMMAcopolymers are commercially available, e.g. with the trademarksPleximid® or Plexiglas® from Röhm. One example of a copolymer (PLEXIMID8803) has 33% of MMI units, 54.4% of MMA units and 2.6% of methacrylicacid units, and 1.2% of anhydride units.

[0025] The poly(N-methylmethacrylimides) used may in particular be thosewhich have at least the following constituents:

[0026] i) from 14 to 85 parts by weight, preferably from 30 to 70 partsby weight

[0027] ii) from 10 to 75 parts by weight, preferably from 20 to 40 partsby weight

[0028] iii) from 0 to 15 parts by weight

[0029] iv) from 1 to 20 parts by weight, preferably from 2 to 12 partsby weight

[0030] In the formulae mentioned

[0031] R¹ to R⁵ are identical or different aliphatic or alicyclicradicals having from 1 to 40 carbon atoms, preferably —CH₃.

[0032] The copolymers are termed polymethacrylimides, and sometimes alsopolyglutarimides. These are polymethyl (meth)acrylates in which twoadjacent carboxyl(ate) groups have been reacted to give a cyclic imide.The preferred method of imide formation uses ammonia or primary amines,e.g. methylamine. The products are known, as is their preparation (HansR. Kricheldorf, Handbook of Polymer Synthesis, Part A, Verlag MarcelDekker Inc. New York—Basle—Hong Kong, pp. 223 et seq.; H. G. Elias,Makromoleküle, Hüthig und Wepf Verlag Basle—Heidelberg—New York; U.S.Pat. Nos. 2,146,209 and 4,246,374).

[0033] Sinter powders of the invention may comprise flow aids or elseother auxiliaries and/or fillers, and/or pigments. These auxiliaries maybe fumed silica or else precipitated silicas, for example. Fumed silicais supplied by way of example with the product name Aerosil®, withvarious specifications, by Degussa AG. Sinter powder of the inventioncomprises less than 3% by weight, preferably from 0.001 to 2% by weight,and very particularly preferably from 0.05 to 1% by weight of thesefillers, based on the entirety of the polymers present, i.e. theentirety of polyamides, PMMA, PMMI, and/or PMMI-PMMA copolymers.Examples of the fillers are glass particles, aluminum particles, metalparticles, or ceramic particles, e.g. solid or hollow glass beads, steelshot, or granulated metal, or else color pigments, e.g. transition metaloxides.

[0034] The grain size of the filler particles here is preferably smallerthan or approximately equal to the grain size of the particles of thepolyamides. The median grain size d₅₀ of the fillers should preferablynot exceed the median grain size d₅₀ of the polyamides by more than 20%,with preference 15%, and with very particular preference 5%. Aparticular limitation on the particle size results from the permissibleoverall height or, respectively, layer thickness in the laser-sinteringapparatus.

[0035] Sinter powder of the invention preferably comprises less than 70%by weight, with preference from 0.001 to 60% by weight, with particularpreference from 0.05 to 50% by weight, and with very particularpreference from 0.5 to 25% by weight, of these fillers, based on theentirety of the polymers present, the proportion of the polymers byvolume therefore always being greater than 50%.

[0036] If the stated maximum limits for auxiliaries and/or fillers areexceeded, depending on the filler or auxiliary used, the result can bemarked impairment of mechanical properties of moldings produced fromthese sinter powders. The excess can moreover disrupt the intrinsicabsorption of laser light by the sinter powder, making this powderunusable for selective laser-sintering.

[0037] The sinter powders of the invention can be prepared simply, andpreferably by the process of the invention for preparing sinter powderof the invention by mixing at least one polyamide with at least one PMMIor PMMA or PMMI-PMMA copolymer. Dry mixing or mixing in suspension maybe used. In a preferred method, a polyamide powder obtained, forexample, by reprecipitation and/or milling, which may also then befractionated, is mixed with PMMI, PMMA and/or PMMI-PMMA copolymerpowder. The polyamide may moreover be compounded with PMMI, PMMA, and/orPMMI-PMMA copolymer to give a sinter powder and then be milled. Anotherpossible embodiment suspends the polyamide in the presence of a solventin which the PMMI or PMMA or PMMI-PMMA copolymer has at least somedegree of solubility, and mixes it with PMMI, PMMA, and/or PMMI-PMMAcopolymer, and then removes the dispersion medium/solvent.

[0038] In the simplest embodiment of the process of the invention, afine-particle mixture may be obtained, for example, by using a mixingprocess to apply a fine powder of PMMI, of PMMA, or of PMMI-PMMAcopolymer to the dry polyamide powder in high-speed mechanical mixers,or by a wet-mixing process in low-speed assemblies—e.g. paddle dryers orcirculating screw mixers (known as Nauta mixers)—or by dispersion ofPMMI, PMMA, and/or PMMI-PMMA copolymer and polyamide (powder) in anorganic solvent followed by distillative removal of the solvent.Examples of solvents suitable for this variant are lower alcohols havingfrom 1 to 3 carbon atoms, and ethanol may preferably be used as solvent.

[0039] In one of these first variants of the process of the invention,the polyamide powder may be a polyamide powder which is in itself asuitable laser-sintering powder, and with which fine particles of PMMI,of PMMA, or of PMMI-PMMA copolymer are simply admixed. The particlespreferably have approximately the same median grain size as theparticles of the polyamides. The median grain size of the particles ofPMMI, particles of PMMA, and/or particles of PMMI-PMMA copolymer ispreferably within 20%, with preference within 15%, and very particularlypreferably within 5%, of the median grain size d₅₀ of the polyamideparticles or, respectively, polyamide powders. The grain size is inparticular subject to a limit by virtue of the permissible overallheight or, respectively, layer thickness in the laser-sinteringapparatus.

[0040] It is also possible to mix conventional sinter powders withsinter powders of the invention. This method can give sinter powderswith an ideal combination of mechanical and optical properties. Theprocess for preparing these mixtures can be found by way of example inDE 34 41 708.

[0041] In another variant of the process, PMMI, PMMA, and/or PMMI-PMMAcopolymer is mixed with a, preferably molten, polyamide, usingincorporation by compounding, and the resultant PMMI-, PMMA-, and/orPMMI-PMMA-copolymer-containing polyamide is processed by(low-temperature) milling and, where appropriate, fractionation, to givelaser-sintering powder. The compounding process usually gives pelletswhich are then processed to give sinter powder, generally bylow-temperature milling. That variant of the process in which PMMI,PMMA, and/or PMMI-PMMA copolymer is incorporated by compounding has theadvantage over the straight mixing process of achieving more homogeneousdistribution of the PMMI and/or PMMA, and/or PMMI-PMMA copolymer in thesinter powder.

[0042] Where appropriate, to improve the flow behavior of the powder ofthe invention, a suitable flow aid, such as fumed aluminum oxide, fumedsilica, or fumed titanium dioxide, may be added externally to theprecipitated or low-temperature milled powder.

[0043] In another variant of the process, PMMI, PMMA, and/or PMMI-PMMAcopolymer in the form of powder is admixed with the polyamide before theprecipitation process is complete, preferably within the freshlyprecipitated suspension. This type of precipitation process is describedby way of example in DE 35 10 687 and DE 29 06 647.

[0044] The person skilled in the art can also apply this variant of theprocess in a modified form to other polyamides, by selecting polyamideand solvent in such a way that the polyamide dissolves in the solvent atan elevated temperature and precipitates from the solution at a lowertemperature and/or on removal of the solvent. The correspondingpolyamide laser-sintering powders of the invention are obtained byadding PMMI, PMMA, and/or PMMI-PMMA copolymer, preferably in the form ofparticles, to this solution, and subsequent drying.

[0045] The PMMI, PMMA and/or PMMI-PMMA copolymers used may becommercially available products, for example those which can bepurchased from Röhm with the trademark Pleximid® or Plexiglas®, or maybe those described above.

[0046] Materials which may be added to the sinter powder to improveprocessability or for its further modification are inorganic pigments,in particular color pigments, e.g. transition metal oxides, stabilizers,e.g. phenols, in particular sterically hindered phenols, flow aids, e.g.fumed silicas, and also particulate fillers. The amount of thesesubstances added to the polyamide, based on the total weight ofpolyamides in the sinter powder, is preferably such as to comply withthe concentrations stated for fillers and/or auxiliaries for the sinterpowder of the invention.

[0047] The present invention also provides a process for producingmoldings by selective laser-sintering, using sinter powders of theinvention comprising polyamide and PMMA or PMMI, i.e. partially imidatedPMMA, or copolymers thereof, particularly in particulate form. Thepresent invention in particular provides a process for producingmoldings by selective laser-sintering of a PMMI-, PMMA-, orPMMI-PMMA-copolymer-containing precipitation powder based on a nylon-12which has a melting point of from 185 to 189° C., an enthalpy of fusionof 112±17 J/g, and a freezing point of from 136 to 145° C., the use ofwhich is described in U.S. Pat. No. 6,245,281.

[0048] Laser-sintering processes are well-known, and are based on theselective sintering of polymer particles, layers of polymer particlesbeing briefly exposed to laser light, thus causing the polymer particleswhich have been exposed to the laser light to become bonded to oneanother. Successive sintering of layers of polymer particles producesthree-dimensional objects. Details of the selective laser-sinteringprocess are found by way of example in the specifications U.S. Pat. No.6,136,948 and WO 96/06881.

[0049] The moldings of the invention produced by selectivelaser-sintering comprise at least PMMI, PMMA, and/or PMMI-PMMAcopolymer, and at least one polyamide. The moldings of the inventionpreferably comprise at least one polyamide which has at least 8 carbonatoms per carboxamide group. Moldings of the invention very particularlypreferably comprise at least one nylon-6,12, nylon-11, and/or nylon-12,and PMMI, PMMA, and/or PMMI-PMMA copolymers.

[0050] The PMMI present in the molding of the invention is based on PMMAwhich has been partially cycloimidized, or PMMA, or copolymer of PMMIand PMMA. The molding of the invention preferably comprises, based onthe entirety of the polymers present in the molding, from 0.01 to 30% byweight of PMMI, PMMA, and/or PMMI-PMMA copolymer, with preference from0.1 to 20% by weight, and with particular preference from 0.5 to 15% byweight, and with very particular preference from 1 to 12% by weight. Theproportion of PMMI, PMMA, and PMMI-PMMA copolymer is not more than 30%by weight, based on the entirety of the polymers present in the molding.

[0051] The moldings may moreover comprise fillers and/or auxiliaries,and/or pigments, e.g. heat stabilizers, and/or antioxidants, e.g.,sterically hindered phenol derivatives. Examples of fillers are glassparticles, ceramic particles, and also metal particles, e.g., ironspheres, and/or corresponding hollow spheres. The moldings of theinvention preferably comprise glass particles, very particularlypreferably glass beads. Moldings of the invention preferably compriseless than 3% by weight, with preference from 0.001 to 2% by weight, andvery particularly preferably from 0.05 to 1% by weight, of theseauxiliaries, based on the entirety of the polymers present. Moldings ofthe invention also preferably comprise less than 75% by weight, withpreference from 0.001 to 70% by weight, with particular preference from0.05 to 50% by weight, and with very particular preference from 0.5 to25% by weight, of these fillers, based on the entirety of the polymerspresent.

[0052] The examples below are intended to describe the sinter powder ofthe invention and its use, but no restriction of the invention to theexamples is intended.

EXAMPLES

[0053] The BET surface area determination that was performed, asdescribed in the examples below, complied with DIN 66131. Bulk densitywas determined using an apparatus to DIN 53466. Laser scattering wasmeasured on a Malvern Mastersizer S, using version 2.18. Beamcompensation was determined using an internal specification, and it wasused as a measure of precision of reproduction. The smaller the beamcompensation, the greater the accuracy of reproduction of a structureusing the laser beam. When this method was used, a laser-sinteringmachine constructed specimens of varying lengths, which were 10 mm wideand 3 mm thick. The lengths were 5, 8, 10, 20, 50, and 100 mm. To makehandling easier, there is a narrow fillet connecting these specimens toone another. The components were placed in the four comers of themanufacturing chamber. The individual sets were in each case rotated by90 degrees with respect to the others. A slide gauge was used to measurethe length of the specimens, in each case at the sides and centrally,the measured values for the 4 components were averaged, and then therequired values and actual values were plotted graphically against oneanother. A straight line was drawn through these points, and the valuefor beam compensation (in mm) was obtained, this being the point ofintersection representing the shift of the straight line from the origin(constant in the equation for the straight line).

Example 1. Preparation of Laser-Sintering Powder With No PMMI

[0054] 40 kg of unregulated PA 12, which was prepared by hydrolyticpolymerization by a method based on DE 35 10 691, Example 1, with arelative solution viscosity 7η_(rel) of 1.61 (in acidified m-cresol) andwith an end group content of 72 mmol/kg of COOH and 68 mmol/kg of NH₂,were heated to 145° C. with 0.3 kg of Irganox® 1098 in 350 L of ethanoldenaturated with 2-butanone and 1% water content within a period of 5hours in a 0.8 m³ stirred vessel (diameter=90 cm, height=170 cm), andheld for 1 hour at this temperature with stirring (blade stirrer: bladediameter=42 cm, blade rotation=91 rpm). The jacket temperature was thenreduced to 120° C., and the internal temperature was brought to 120° C.,using a cooling rate of 45 K/h, with the same stirrer rotation rate.While using the same cooling rate, the jacket temperature was maintainedat a level of from 2 to 3 K below the internal temperature. The internaltemperature was brought to 117° C., using the same cooling rate, andthen held constant for 60 minutes. The internal temperature was thenbrought to 111° C., using a cooling rate of 40 K/h. At this temperatureprecipitation began, which was detectable by heat generation. After 25minutes the internal temperature fell, which indicated that theprecipitation had ended. After the suspension was cooled at 75° C., thesuspension was transferred to a paddle dryer. The ethanol was distilledoff from the mixture with stirring at 70° C./400 mbar and the residuewas then further dried for 3 hours at 20 mbar/85° C. TABLE 1 Sieveanalysis of laser-sintering powder with no PMMI Particle Size, μm % bywt. <32 7 <40 16 <50 44 <63 85 <80 92 <100 100

[0055] BET: 6.9 m²/g

[0056] Density: 429 g/L

[0057] Laser scattering: d(10%): 42 μm, d(50%): 69 μm, d(90%): 91 μm

Example 2. Preparation of Laser-Sintering Powder by Incorporation ofPMMI (PLEXIMID 8813) by Compounding Followed by Milling

[0058] 40 kg of regulated VESTAMID L1600 PA 12 from Degussa AG, preparedby hydrolytic polymerization, were extruded with 0.3 kg of Irganox® 245and 0.8 kg of PMMI (PLEXIMID 8813, Röhm GmbH) at 225° C. in a twin-screwcompounder (Berstorf ZE25), and strand-pelletized. The pellets were thenmilled at low temperatures (−40° C.) in an impact mill to give a grainsize distribution from 0 to 120 μm. 40 g of Aerosil 200 (0.1 part) werethen mixed into the material for 3 minutes at 500 rpm and roomtemperature.

Example 3. Preparation of Laser-Sintering Powder by Incorporation ofPMMI (PLEXIMID 8813) PMMI in a Dry Blend

[0059] The dry blend process, which utilized a FML10/KM23 Henschel mixerfor 3 minutes at 50° C. and 700 rpm, was used to mix 100 g (5 parts) ofPLEXIMID 8813 with 1900 g (95 parts) of nylon-12 powder prepared inaccordance with DE 29 06 647, Example 1, with a median grain diameterd₅₀ of 56 μm (laser scattering) and with a bulk density of 459 g/L toDIN 53466. 2 g of Aerosil 200 (0.1 part) were then mixed into thematerial within 3 minutes at room temperature.

[0060] The same conditions were used to prepare other powders having 0,1, 3, 4, and 10% of PLEXIMID 8813.

[0061] Further processing:

[0062] The powders from Example 3 were used on a laser-sintering machineto construct the test specimens described above for determining beamcompensation, and to construct a multipurpose specimen to ISO 3167. Atensile test to EN ISO 527 was used to determine mechanical values onthe latter components. Each production took place on an EOSINT P360laser-sintering machine from EOS GmbH. TABLE 2 Properties oflaser-sintering powder with added PLEXIMID 8813. Modulus Tensile Tensileof specimen specimen Tensile Beam elasticity Tensile strain thickness,width, strength, PMMI compensation N/mm² at break % mm mm N/mm² 0% 0.821633 20.7 4.38 10.61 46.6 1% 0.79 1646 19.1 4.34 10.60 46.1 3% 0.77 179016.9 4.21 10.63 49.2 4% 0.77 1812 14.6 4.05 10.59 49.4 10% 0.73 1839 7.94.07 10.51 47.7

[0063] It is clearly seen that increased addition of PMMI to thelaser-sintering powder permits production of moldings with markedlylower beam compensation. Increased addition of PMMI moreover increasesmodulus of elasticity, while at the same time reducing tensile strain atbreak. Furthermore, as the content of the PMMI increases, the dimensionsof the moldings approximate ever more closely to the required value,which is 4 mm for tensile specimen thickness and 10 mm for tensilespecimen width.

[0064] The priority document of the present application, DE application103 11 437.8, filed Mar. 15, 2003, is incorporated herein by reference.

[0065] Obviously, numerous modifications and variations on the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and is intended to be secured by a Letters Patentis:
 1. A sinter powder for selective laser sintering, which comprises:at least one polyamide and at least one poly(N-methylmethacrylimide)(PMMI), one polymethyl methacrylate (PMMA), and/or one PMMI-PMMAcopolymer.
 2. The sinter powder as claimed in claim 1, which furthercomprises: a polyamide which comprises at least 8 carbon atoms percarboxamide group.
 3. The sinter powder as claimed in claim 1, whichfurther comprises: an unregulated polyamide.
 4. The sinter powder asclaimed in claim 1, which further comprises: at least one nylon which isselected from the group consisting of nylon-6,12, nylon-11, nylon-12, acopolyamide; wherein said copolyamide is based on the named nylons, andmixtures thereof.
 5. The sinter powder as claimed in claim 1, whereinthe PMMI, PMMA and/or PMMI-PMMA copolymer ranges from 0.01 to 30 wt. %,which is based on the entirety of the polymers present in the powder. 6.The sinter powder as claimed in claim 1, wherein the PMMI, PMMA and/orPMMI-PMMA copolymer ranges from 0.5 to 15 wt. %, which is based on theentirety of the polymers present in the powder.
 7. The sinter powder asclaimed in claim 1, which further comprises a mixture of particles ofPMMI, of PMMA, or of PMMI-PMMA copolymer, with particles of polyamide.8. The sinter powder as claimed in any of claim 1, which furthercomprises polyamide particles into which PMMI, PMMA, and/or PMMI-PMMAcopolymer has been incorporated.
 9. The sinter powder as claimed inclaim 1, which further comprises one or more auxiliary, and/or filler,and/or pigment.
 10. The sinter powder as claimed in claim 9, wherein theauxiliary comprises a flow auxiliary.
 11. The sinter powder as claimedin claim 9, wherein the filler comprises glass particles.
 12. The sinterpowder as claimed in claim 9, wherein the filler comprises aluminumparticles.
 13. A process for preparing the sinter powder as claimed inclaim 1, which comprises: mixing at least one polyamide with at leastone PMMI, one PMMA, and/or one PMMI-PMMA copolymer.
 14. The process asclaimed in claim 13, which further comprises mixing a polyamide powderobtained by reprecipitation or milling, in suspension or in solution inan organic solvent, or in bulk, with PMMI, PMMA, or PMMI-PMMA copolymer.15. The process as claimed in claim 13, which further comprisescompounding the PMMI, PMMA, and/or PMMI-PMMA copolymer into a melt ofpolyamide; followed by milling the resultant mixture to give a lasersinter powder.
 16. A process for producing moldings, which comprises:selectively laser sintering the sinter powder as claimed in claim
 1. 17.A molding produced by laser sintering, which comprises: at least onePMMI, one PMMA, and/or one PMMI-PMMA copolymer, and at least onepolyamide.
 18. The molding as claimed in claim 17, which furthercomprises a polyamide which has at least 8 carbon atoms per carboxamidegroup.
 19. The molding as claimed in claim 17, which further comprisesnylon-6,12, nylon-11 and/or nylon-12.
 20. The molding as claimed inclaim 18, which further comprises nylon-6,12, nylon-11 and/or nylon-12.21. The molding as claimed in claim 17, wherein the PMMI, PMMA and/orPMMI-PMMA copolymer ranges from 0.01 to 30 wt. %, which is based on theentirety of the polymers present in the powder.
 22. The molding asclaimed in claim 17, wherein the PMMI, PMMA and/or PMMI-PMMA copolymerranges from 0.5 to 15 wt. %, which is based on the entirety of thepolymers present in the powder.
 23. The molding as claimed in claim 17,which further comprises fillers and/or pigments.
 24. The molding asclaimed in claim 23, wherein at least one of the fillers is glassparticles.
 25. The molding as claimed in claim 23, wherein at least oneof the fillers is aluminium particles.